The present invention relates to an electronic control system for performing remote control over a car or vehicle with use of a radio signal such as radio wave or infrared ray, called keyless entry and more particularly, to an electronic control system for car remote control which switches between its sleep and operational modes as well as to a multiplex communication system employed for the electronic control system.
As a system for controlling supply of power to this type of electronic control system not having a remote control function, it is known as disclosed in JP-A-63-71451 to stop a terminal clock when power supply is unnecessary.
Also disclosed in JP-A-5-32142 is a system, when a microcomputer-controlled system is put in its sleep mode, for also causing a power supply for a watch dog timer to be automatically turned OFF, thus realizing reduction in its current consumption. Further, when it is desired to provide a remote control function to the electronic controller, such a power control system as to follow is considered.
An exemplary schematic arrangement of the power control system is shown in FIG. 1 wherein reference numeral 50' denotes an electronic controller. An antenna 54' receives a radio wave signal issued from a transmitter T carried by a car driver and sends the radio wave signal to a tuner 55'. The tuner 55' in turn, when receiving the radio wave signal from the antenna 54', modulates the radio wave signal into a digital signal and sends the digital signal to a microprocessor unit (MPU) 56'. The MPU 56' judges the signal received from the tuner 55' to control a trunk lid opener motor 60' or the like. Numeral 58' denotes a low-frequency oscillation circuit and numeral 59' denotes a high-frequency oscillation circuit. The MPU operates with a high frequency clock received from the high-frequency oscillation circuit 59' for the purpose of performing high-speed calculating operation in a usual operational mode; whereas, the MPU operates with a low frequency clock received from the low-frequency oscillation circuit 58' for the purpose of suppressing current consumption in a sleep mode. Control signals 62' and 63' act to stop the low- and high-frequency oscillation circuits 58' and 59' respectively. In the illustrated example, even in the sleep mode, the MPU operates at a low speed to monitor the signal received from the tuner.
Such another system as shown in FIG. 2 is also considered. That is, the system is arranged so that the output signal of the tuner 55' is processed by a signal processing circuit 65 not by the MPU 56' to be applied to the MPU as a wake-up signal and a control signal for the MPU.
With the above prior art control unit for receiving the radio wave signal and controlling power supply based on the received signal, various types of electromagnetic waves are present in the air so that, even when the tuner fails to receive the normal radio wave signal, the tuner can issue an output signal. To avoid this, power supply to the tuner is intermittently carried out from an intermittent power supply 53' shown in FIG. 1 or 2 to reduce a current to be consumed by the tuner. Further, for preventing noise from waking up the control unit, the unit judges whether or not the output signal of the tuner is normal on the basis of only first part of the entire tuner output signal within a time duration shorter than an intermittent time duration. When the control unit judges that the tuner output signal is normal, the control unit shifts the clock of the MPU to a higher frequency clock for usual operation and also causes the intermittent power supply circuit to supply power continuously in the example of FIG. 1. In the example of FIG. 2, when a processing circuit 65 judges that the tuner signal is normal, the MPU starts its operation to perform the usual operation, and also causes the intermittent power supply 53' to supply power continuously. Since the tuner signal having such a waveform as shown in FIG. 3 is judged as not normal, the MPU will not perform the usual operation. When the tuner signal is such a pulse signal having a relatively wide pulse width as shown in FIG. 4 and first one (A) of pulses in the pulse signal is normally input, on the other hand, the MPU performs the usual operation and causes the intermittent power supply 53' to continuously supply power to the tuner, thus reducing current consumption. In either example, in order to judge whether or not the tuner signal is normal, the oscillation circuits of the MPU are required in the example of FIG. 1 while the oscillation circuit of the processing circuit is required in the example of FIG. 2. In addition, even when the pulses in the tuner signal are followed by a noise pulse signal having a relatively small pulse width as in FIG. 4, that is, even when it is later judged as unnecessary to start or wake up the MPU, the MPU is already put in the usual control operation after the once normal judgement. For this reason, the MPU can be put in the sleep mode only after a re-sleeping procedure is carried out. In this way, in the prior art, the low-frequency oscillation circuit is operated even in the sleep mode so that, even when it is unnecessary to wake up the system, the entire system is put in the usual operation, thus disabling realization of sufficiently reduced current consumption.